Pixel binning combines multiple small sensor pixels into one larger virtual pixel, improving low-light performance at the cost of resolution. A 48 MP sensor often outputs 12 MP photos by 4-in-1 binning.
When pixels are binned 2×2 (4-in-1), a 48 MP sensor outputs 12 MP images with effectively 4× larger pixels. Larger pixels gather more light per pixel, reducing noise.
Most flagship phones default to binned mode for everyday photos and offer a "high resolution" mode for full sensor capture in good light.
Samsung's Tetracell (4-in-1) and Sony's Quad Bayer technologies enable this. Newer 200 MP sensors (Samsung HP3, ISOCELL HP1) bin 16-in-1 for 12.5 MP output, or 4-in-1 for 50 MP.
Tradeoff: binned photos handle low light well; full-res photos preserve detail in bright conditions.